bug#48011: 27.2; Emacs freezes in modula 2 mode when entering a :

[Gregory Heytings]

> > This is a forward of 
> > https://bugzilla.redhat.com/show_bug.cgi?id=1950158 Emacs 27.2 freezes 
> > when editing a file that ends with .mod (i.e. it opens the file in 
> > Modula 2 mode) after one enters a ':'. The UI simply hangs until one 
> > interrupts it with C-g.
>
> First, I was super happy to see a bug report about modula2.el's 
> indentation code (which I kind of presumed was never used).

Alas, the original bug report says: "I'm not actually programming in 
Modula-2, but the product I'm using typically names files with the .mod 
suffix."

> But I'm starting to think that the real problem here is that you 
> actually didn't open a Modula-2 file.
>
> What kind of file was that `.mod` file?

Why is this important?  Even if the file is not actually a Modula-2 file, 
Emacs should not freeze when the user types ":": with emacs -Q foo.mod, 
type "a:", and Emacs freezes (until the user presses C-g).